The present invention relates to a vacuum gate valve comprising a closure disk for substantially gas-tight closing of an opening by displacement of the closure disk over the opening and pressing of the closure disk onto the opening by means of at least two limbs.
Different embodiments of vacuum valves for substantially gas-tight closing of a flow path which leads through an opening in a valve housing are disclosed in the prior art. Particularly in the area of IC and semiconductor manufacture, which must take place in a protected atmosphere as far as possible without the presence of contaminating particles, vacuum gate valves, also referred to as vacuum gates, are used. For example, in a production plant for semiconductor wafers or liquid crystal substrates, the highly sensitive semiconductor or liquid crystal elements pass sequentially through a plurality of process chambers in which the semiconductor elements present inside the process chamber are processed by means of in each case a processing apparatus. Both during the processing inside the process chamber and during the transport from process chamber to process chamber, the highly sensitive semiconductor elements must always be present in a protected atmosphere—in particular in an environment free of air. The process chambers are connected to one another, for example, via connecting corridors, it being possible for the process chambers to be opened by means of vacuum gate valves for transfer of the parts from one manufacturing chamber to the next and to be closed gas-tight after the respective manufacturing step has been carried out. Such vacuum gate valves are also referred to as vacuum transfer valves owing to the field of use described and the associated dimensioning and are also referred to as rectangular gates owing to their rectangular opening cross-section.
The prior art discloses various embodiments of vacuum valves, in particular the sealing and drive technology thereof. Depending on the respective drive technologies, a distinction is made in particular between vacuum gate valves or gate valves, also referred to as valve gates or rectangular gates, and shuttle valves, the closing and opening generally taking place in two steps.
In a first step, a valve closure, in particular a closure disk, is displaced linearly over an opening substantially parallel to the valve seat in the case of gate valve, as disclosed, for example, in U.S. Pat. No. 6,416,037 (Geiser) or U.S. Pat. No. 6,056,266 (Blecha), or is pivoted about an axis of rotation over the opening in the case of a shuttle valve, as disclosed, for example, in U.S. Pat. No. 6,089,537 (Olmsted), without contact between the closure disk and the valve seat of the valve housing taking place thereby. In a second step, the closure disk is pressed with its closure side onto the valve seat of the valve housing so that the opening is closed gas-tight. The sealing can be effected, for example, either via a gasket which is arranged on the closure side of the closure disk and pressed onto the valve seat running around the opening, or via a gasket on the valve seat, against which the closure side of the closure disk is pressed.
Different sealing devices are disclosed in the prior art, for example in U.S. Pat. No. 6,629,682 B2. A suitable material for gaskets is, for example, the resilient sealing material known by the trade name Viton®.
The closing movement of a gate valve which takes place in two steps can be achieved by means of different mechanisms. The valve closure mounted, for example, on two connecting rods is connected via the connecting rods to a drive mechanism which, by a substantially linear movement along the connecting rod axis, permits a displacement of the closure disk substantially parallel above the opening to be closed. By means of the same drive mechanism, it is possible, by pivoting of the connecting rods, to swivel the closure disk, which is now present in a position opposite the opening and a distance away and substantially parallel to the valve seat, in the direction of the valve seat and to press it substantially perpendicularly onto the valve seat. Instead of two connecting rods, it is also possible to use only one connecting rod. The use of a plurality of connecting rods is likewise possible.
The prior art discloses different types of such drive mechanisms, which in each case may result in a slightly different displacement path of the connecting rod and hence of the closure disk. Thus, for example, instead of swivelling of the closure disk along an arc on the valve seat, an absolutely linear movement of the closure disk perpendicular to the valve seat can be initiated. Drive mechanisms which permit both a substantially linear displacement of the closure disk above the opening and substantially perpendicular pressing of the closure disk onto the valve seat running around the opening are disclosed, for example, in U.S. Pat. No. 6,431,518 B1, U.S. Pat. No. 5,415,376 A, U.S. Pat. No. 5,641,149 A, U.S. Pat. No. 6,045,117 A, U.S. Pat. No. 5,934,646 A, U.S. Pat. No. 5,755,255 A, U.S. Pat. No. 6,082,706, U.S. Pat. No. 6,095,180 and U.S. Pat. No. 6,629,682 B2.
By means of the closing process taking place in two steps, it is intended that the gasket be subjected to scarcely any sheer forces which would destroy the gasket, since a substantially linear movement of the closure disk perpendicularly onto the valve seat takes place as a result of the swivelling of the connecting rods.
The two-stage movement sequence can, however, also be achieved by means of a plurality of separate drive mechanisms. For example, U.S. Pat. No. 6,056,266 (Blecha) and U.S. Pat. No. 6,561,484 (Nakagawa) describe gate valves whose connecting rods are linearly displaceable only along the connecting rod axis, with the result that the closure disk can be displaced parallel above the opening without having any contact between the closure disk and the valve seat. The drive mechanism can in this case be formed by a simple linear movement drive, for example a cylinder drive. The pressing of the closure disk onto the valve seat is achieved by a separate drive in the two-part closure disk or between the closure disk and the connecting rods. This separate drive is in particular in the form of a cylinder drive by means of which the closing side of the closure disk can be pressed linearly and perpendicularly onto the valve seat, as shown in U.S. Pat. No. 6,056,266 (Blecha).
U.S. Pat. No. 6,561,483 (Nakagawa) and U.S. Pat. No. 6,561,484 (Nakagawa et al.) disclose gate valves in different embodiments which comprise a two-part closure disk. A first disk section has an opening. A second disk section is connected by means of an extendable body to the first disk section. An actuator is arranged between the first and second disk section so that the two disk sections can be actively moved toward one another and away from one another. The extensible body is in the form of a bellows. The first disk section can be pressed against the valve seat by means of the actuator, the second disk section—in particular in the case of excess pressure on the valve seat side—optionally being supported on an opposite valve housing side. The design of such vacuum valves having drives in the closure disk is relatively complex especially because of the necessity of using a bellows or a plurality of sealing rings for sealing the first disk section to the second disk section and to the valve seat, is disadvantageous regard to maintenance and is susceptible to soiling.
A general disadvantage of said vacuum valves is in general the relatively complex design of the at least one drive mechanism which must permit the above-described two movements, which as far as possible are linear, in two directions substantially at right angles to one another.
U.S. Pat. No. 5,769,952 (Komino) discloses a gate valve which is in the form of a vacuum transfer valve and is composed substantially of a linear displacement drive, a connecting rod linearly displaceable along its connecting rod axis and a closure disk. The closure disk is connected via two limbs to the connecting rod. By displacement of the connecting rod linearly along the connecting rod axis in the closing direction, the closure disk can be displaced parallel above the valve opening, the closure disk being present opposite to and a distance away from the valve seat which surrounds the opening. The two limbs are each mounted at one limb end on a crossbar extending transversely to the connecting rod and running parallel to the plane of the valve seat and are each mounted at the other limb end in a pivotable manner on the closure disk by means of pivot bearings. Both limbs are arranged parallel to one another in the direction of the crossbar and have in each case a common geometrical axis of rotation with respect to the closure disk and with respect to the crossbar. The limbs hold the closure disk in such a way that the geometrical axis of rotation on the cross bar side is present below the axis of rotation on the closure part side with respect to the closing direction of the linear displacement direction of the connecting rod, so that a force acting on the closure disk against the closing direction of the connecting rod leads to a reduction of the distance between the two axes of rotation with respect to the closing direction. A guide roller is arranged at the end of the linear displacement path of the closure disk. If there is contact between the closure disk and the guide roller, the closure disk can no longer be displaced further in the closing direction. However, the linear displacement drive continues to exert a force on the closure disk so that the limbs can swivel out, thus approach the perpendicular position to the linear displacement direction and act as a lever. Thus, the closure disk is displaced in the direction of the valve seat and is pressed onto the latter.
An advantage of such a gate valve having a limb mechanism is the relatively simply designed drive, since the connecting rod need only be displaced linearly. However, the forces which act perpendicularly on the connecting rod axis and have to be absorbed by the connecting rod bearing present a problem. Since the closure disk is supported on the guide roller and must therefore absorb large forces, the closure disk must be designed with large dimensions. Owing to the arrangement of the axes of rotation, the parallel alignment of the closure disk with the valve seat is not ensured, and the closure disk therefore initially rests skew on contact with the valve seat, shear forces on the seal are unavoidable and a uniformly distributed contact force is not ensured. By using the guide roller and the pivot bearing, the generation of particles, in particular owing to friction, cannot be prevented, and freedom from particles is therefore not ensured.
JP 60222670 describes a vacuum gate valve in which a closure part is mounted on a linearly displaceable connecting rod by means of two limbs which are pivotable in the manner of a parallelogram and are parallel and a distance apart in the displacement direction of the connecting rod. Owing to the mounting in the manner of a parallelogram via the limbs, the closure part is always aligned parallel to the connecting rod and to the valve seat. When the closure part is swivelled out in the closing direction of the linearly displaceable connecting rod, the closure part is moved by linear displacement of the connecting rod parallel above the opening of the valve until the closure part touches a stopper mounted above the opening. The stopper prevents the closure part from further movement in the closing direction. However, since the connecting rod is further displaced in the closing direction, the limbs swivel out in the direction of the valve seat so that the closure part is pressed onto the valve seat and the opening is thus closed.
In the case of the valve described in JP 60222670, the limbs are mounted on the connecting rod and the closure part by means of bolts. The pivot mechanism described thus has a multiplicity of friction points at which abrasion particles are produced owing to a relative frictional movement. For this reason, such a pivot mechanism is substantially unsuitable for fields of use in which particle generation must be kept to a minimum.
U.S. Pat. No. 4,491,145 (Williams et al.), U.S. Pat. No. 5,415,375 (Gaboriault), U.S. Pat. No. 2,841,361 (Palmer) and GB 257, 254 also describe gate valves having such parallelogram-guided mechanically mounted limbs for pressing a valve closure onto a valve seat by the swivelling out of the limbs. Common to these embodiments is that, owing to their numerous friction points, in particular the bearings of the limbs, their operation is associated with relatively considerable particle production and use in the high-cleanliness vacuum sector in which the free particles are to be kept to a minimum is substantially ruled out.
The requirement for a vacuum valve of the type mentioned at the outset, in particular a vacuum transfer valve, which has a relatively simple drive and meets the general requirements, which are very high in vacuum technology and in particular in semiconductor production, for a vacuum valve, in particular with respect to as little particle generation as possible, could therefore not be met to date to the desired extent.